In complex electrical supply systems bundles of electrical wires, tied together at intervals along their length by cable ties, are retained in ducts or channels to prevent entanglement, damage or interaction with other parts of the system. During assembly, wires may be fed into elongate ducts from one end or retained in open channels. The latter arrangement is preferred in some modern systems. The use of such open channels facilitates access and maintenance, but means that additional means must be provided to retain the wires within the channels while reducing to a minimum the risk of chafing or other damage.